Drug-Drug Interaction between Tacrolimus and Fluconazole in a Kidney Transplant Recipient.

We report a case of tacrolimus and fluconazole drug-drug interaction in a 20-year-old female kidney transplant recipient with stable kidney function. The patient's tacrolimus blood concentrations were in the therapeutic range until fluconazole was administrated for Candida albicans infection, on day 58 posttransplant. Tacrolimus blood concentration increased by 125% (18.4 ng/mL) on day 79 and by 212% (25.4 ng/mL) on day 84 posttransplant. On day 92, tacrolimus trough blood concentration returned to the therapeutic range (5.6 ng/mL), with decrease of tacrolimus daily dose by 50% (to 4 mg). After fluconazole withdrawal, the patient was returned to the initial tacrolimus daily dose (8 mg) to maintain a tacrolimus trough blood concentration in the therapeutic range. Fluconazole coadministration with tacrolimus shows a significant clinical effect on tacrolimus trough blood concentration in kidney transplant patients. Maintaining a tacrolimus trough blood concentration in the therapeutic range is crucial for these patients; therefore, physicians should be aware of fluconazole prescriptions.

Interaction Between Tacrolimus and Proton Pump Inhibitor in a Kidney Transplant Recipient.

We aimed to present a drug monitoring profile of tacrolimus and proton pump inhibitor coadministration in a 23-year-old male patient with a history of high blood pressure who underwent kidney transplant. The patient's serum trough levels of tacrolimus were in the therapeutic range until omeprazole 20 mg daily was prescribed. Tacrolimus trough serum level increased to 29.5 ng/mL under the same daily dose and to 13.9 ng/mL after tacrolimus daily dose was decreased to 6 mg/day. This increase in tacrolimus serum level was behind a renal function alteration. After withdrawal of omeprazole, tacrolimus trough serum level returned to the therapeutic range. Because interactions between tacrolimus and omeprazole could result in toxicities, careful monitoring of tacrolimus serum levels should be considered to adjust the dosage.

The effects of the CYP3A5*3 variant on tacrolimus pharmacokinetics and outcomes in Tunisian kidney transplant recipients.

INTRODUCTION: Tacrolimus, exhibits interindividual pharmacokinetic variability and a narrow therapeutic index. The influence of the CYP3A5 6986A>G single nucleotide polymorphism (SNP) on this variability remains a topic of debate. AIM: To assess the impact of the aforementioned SNP on tacrolimus area under curve (AUC0-12h), adverse drug reactions (ADRs), and kidney graft outcomes. METHODS: Blood samples were collected from Tunisian kidney transplants over a five-year period during either the early (<3 months) or late (>3 months) post-transplant phases. Through blood concentration (C0) and AUC0-12h of tacrolimus were measured. Patients were prospectively followed to assess graft outcomes. Polymerase chain reaction of restriction fragment length polymorphism was used for CYP3A5 6986A>G genotyping. RESULTS: Fifty Tunisian kidney recipients receiving tacrolimus were enrolled in the study. Acute and chronic graft rejections were observed in eight and three patients, respectively. Twenty-one patients (42%) reported ADRs. C0 and AUC0-12h, showed a significant difference between CYP3A5*1 carriers (mean C0=4 ng.mL-1 and AUC0-12h=94.37 ng.h.mL-1) and CYP3A5*3/3 or poor metabolizers carriers (mean C0=7.45 ng.mL-1; AUC0-12h=151.27 ng.h.mL-1) (p=0.0001; p=0.003, respectively). Supratherapeutic tacrolimus levels were significantly more common in poor metabolizers (p=0.046; Odds-ratio =1.3; confidence interval 95% [1.12-1.66]). The impact of SNP was significant on C0, AUC0-12h, C0/Dose and AUC0-12h/Dose, only in the late phase (p=0.01, 0.002, 0.012, 0.003 respectively). CONCLUSION: CYP3A5*3 variant was significantly associated with tacrolimus pharmacokinetics but had no impact on graft outcomes.

Comparing real-life carbamazepine exposure between innovator and generic formulation.

BACKGROUND: Carbamazepine is an anticonvulsant largely used in the treatment of epilepsy. The use of generic antiepileptic drugs (AEDs) is controversial because of the eventual possibility to loss seizures control. The aim of our study was to compare the concentration over dose ratio of two products containing carbamazepine, the innovator (Tégrétol®-NOVARTIS) and the generic (Taver®-MEDOCHEMIE). METHODS: It is a retrospective study (2009-2016) including 32 patients treated with carbamazepine. Patients were treated initially by innovator then switched to generic or vice versa. All patients have at least one level of carbamazepine plasma concentration (C0) with the innovator or the generic formulation. Monitoring of carabamazepine was made using immunoassay method (ARCHITECT-ABOTT®). RESULTS: The mean age of our patients was 28.4 years and ranged from 2 to 55 years. The sex ratio M/F was 1.46. The mean ratio C0/dose for the innovator group was 0.723 (min/max: 0.017/1.73), and the mean ratio C0/dose for the generic group was also 0.607 (min/max: 0.064/1.68). There was no statistically significant difference between both groups (P=0.16). CONCLUSION: Our results confirm the difference between the innovator and the generic formulation of carbamazepine. So, switching from innovator to generic seems to be safe and exposure to carbamazepine remains the same.

Is there a ceiling lamotrigine serum level in epileptic children in remission?

INTRODUCTION: Seizure control, in patients with epilepsy, is proportionally associated with health-related quality of life. Antiepileptic therapy leads to seizure remission in most cases. However, some patients are resistant to treatment despite achieving high doses which can be explained by interindividual variability of antiepileptic drugs' metabolism. A ceiling exposure, in epilepsy, helps to adapt the therapeutic strategy in a faster way and to prevent unnecessary exposure to adverse drug reactions. Due to the increasing use of new generations of antiepileptic drugs, we aimed to explore the distribution of lamotrigine (LMT) trough serum levels in epileptic children, stratified between remission and ongoing seizures, in order to determine whether there is a ceiling effect associated with remission. METHODS: We conducted a retrospective study (2012-2021) including children, with generalized epilepsy (2-18 years), addressed for a therapeutic drug monitoring of LMT trough serum levels. Patients in remission, should have as lasting three times the longest pre-treatment seizure-free interval and more than one year. RESULTS: The population of 114 children with generalized epilepsy was divided in to groups: epileptic children in remission (36) and epileptic children with ongoing seizures (78). There was no significant difference in age and sex in the two groups. Median LMT daily dose and trough serum levels were significantly higher in group 2. The highest LMT serum trough level was 11µg/mL in group 1 and 23.1µg/mL in group 2. Valproate was associated in 29%. There was no significant difference of the distribution of valproate in the two groups (P=0.08). CONCLUSIONS: Children in remission had a LMT trough serum levels under 11µg/mL and a daily dose of 3.36mg/kg/day or less. These results suggest that this LMT serum level and daily dose might be associated with a ceiling effect in epileptic children.

Drug interaction between carbamazepine and other antiepileptic drugs in Tunisian epileptic patients.

INTRODUCTION: Carbamazepine could be used on monotherapy or associated to other antiepileptic drugs (AED). In these cases, drug interactions should be taken into account. AIM: To assess the influence of the coadministration of CBZ with other AED on the trough plasmatic concentration (C0) of CBZ in epileptic adults. METHODS: We performed a retrospective study over a period of 9 years in the Department of Clinical Pharmacology in the Tunisian National Centre "Chalbi Belkahia" of Pharmacovigilance. Our study included samples from adult patients receiving CBZ alone or associated to other AED for epilepsy. Trough plasma CBZ plasma concentrations were measured by an immunological method. Included samples were divided in four groups: i/ group 1 (G1) receiving CBZ as monotherapy, ii/ group 2 (G2) treated by CBZ with an enzyme inducer (phenobarbital or phenytoin), iii/ group 3 (G3) taking CBZ associated to an enzyme inhibitor (valproic acid (VPA)), iv/ group 4 (G4), treated by CBZ associated to enzyme inducer (phenobarbital or phenytoin) and enzyme inhibitor (valproic acid) at the same time. RESULTS: There were no significant differences between different groups in age, weight and sex ratio. However statistical analysis showed a significant decrease in C0/D CBZ ratio between G1 and G2 and between G1 and G4 (p<0.001). However, the difference was not significant between G1 and G3 (p=1.2044). CONCLUSION: It is important to check and to prevent the consequences of the interaction between CBZ and other AED in order to avoid inefficiency and toxicity.

Development and validation method for estimation paclitaxel in plasma.

BACKGROUND: Paclitaxel (PTX) is an anticancer drug used in the treatment of many cancer , alone or in combination with other anti-tumors. It has a narrow therapeutic range, a large inter and intra-individual pharmacokinetic variability and haematological toxicity. The most effective pharmacokinetic parameter seems to be the time during which the plasma concentration is over 0.05 µmol/L. AIM: To develop and validate a new method for PTX quantitation in plasma using HPLC with UV/visible detection. METHODS: A rapid HPLC-UV method was developed for the determination of PTX level in plasma. All solvents used were HPLC grade. RESULTS: After liquid-liquid extraction, chromatographic separation was achieved using an RP 18 (250 mm) column. The mobile phase was composed of acetonitrile and 0.1 M potassium dihyrogenophosphate (49/51) (v/v). Clonazepam was used as internal standard. This technique was linear over the range 50 ng/mL to 1500 ng/mL (r= 0.998). The evaluation of precision showed that our method is repeatable with a within-day coefficient of variation (CV) ranging from 6.94 to 18.78 % and reproducible for three studied concentrations low, medium and high with day-to-day CV of 14.92, 10.46 and 11.8% respectively. Under these conditions, each analysis required no longer than 12.81 min. CONCLUSION: We have developed and validate a new assay for PTX monitoring using HPLC with UV detection which is sensible, specific, reliable and easy to carry out in clinical use for its therapeutic drug monitoring.

Early interaction between tacrolimus and rifampin.

Drug interactions are unavoidable and need to be proactively identified and managed, in particular, the inductive effect of rifampin on tacrolimus whose potency and duration data are limited. We report the case of a renal transplant patient who was prescribed tacrolimus with preserved tough blood levels (C0) of 7.9 +/- 2 ng/mL. He presented ganglionic tuberculosis and started rifampin. One day later, C0 was 2.6 ng/mL with 5 mg/day. The serum creatinin was normal. Nine days later, C0 was 1.6 ng/mL with 7 mg/day. In this case-report, the tacrolimus-rifampin interaction occurred just one day after rifampin introduction necessitating early C0 monitoring.

Comparative study of two techniques of mycophenolate mofetyl monitoring.

INTRODUCTION: Mycophenolic acid (MPA) requires routine therapeutic drug monitoring. AIM: To evaluate the suitability of a MPA Immunoassay CEDIA performed on Indiko® analyzer (Thermo fisher) for monitoring of MPA by comparing values obtained by HPLC-UV method. METHODS: This study was carried out on 114 blood samples collected from renal transplant, using high performance liquid chromatography combined with ultraviolet detection (HPLC-UV, reference method) and the new immunoassay on CEDIA. RESULTS: The assay was linear for a mycophenolic acid concentration up to 10 µg/mL. When MPA concentrations in all 114 transplant recipients obtained by the HPLC-UV (x-axis) method were compared with corresponding values obtained by the CEDIA® method (y-axis), the following regression equation was obtained: CEDIA® = 1.558 HPLC + 0.49 (r = 0.86). However more significant positive bias was observed (37 %). CONCLUSION: The data presented suggest that the CEDIA® MPA immunoassay, run on the Indiko® analyzer, over-estimates plasma MPA concentrations. However, CEDIA® immunoassay is less laborious and time consuming than chromatographia techniques.

Limited sampling strategy for the estimation of mycophenolic acid area under the curve in Tunisian renal transplant patients.

Mycophenolate mofetil is a prodrug widely used in renal transplantation to prevent organ rejection. It is hydrolyzed to its active compound mycophenolic acid (MPA). MPA area under the curve (AUC0-12h) is considered the best pharmacokinetic parameter for the estimation of MPA exposition and for prediction of rejection. MPA-AUC requires several blood samples, making it impractical for clinical practice. Therefore, development of a limited sampling strategy (LSS) to estimate MPA AUC0-12h using three blood samples is very helpful for MPA individual dose adjustment. Results of LSS differ according to the patient background and to the drug formulation. Therefore, the purpose of this study was to develop a LSS for the estimation of MPA AUC0-12h in Tunisian renal transplant patients treated with the generic formulation of mycophenolate mofetil (MMF®, MEDIS). The best correlation was achieved by a profile based on three time points C0.5h, C1.5h, and C4h after drug intake: AUC0-12h = 0.414 + 1.210 × C0.5 + 2.256 × C1.5 + 4.134 × C4 (mei = 1.65% and rmse = 5.81%). The correlation between full AUC0-12h and abbreviated AUC0-12h was 0.917. In conclusion, this model provides a reliable and simple equation to estimate MPA AUC0-12h for the generic formulation of mycophenolate mofetil (MMF®).

[Comparative study of two techniques of ciclosporine monitoring]. / Étude comparative de deux techniques de dosage de la ciclosporine.

Ciclosporine (CsA) is an immunosuppressant drug used in bone marrow transplantation in order to extend allograft survival. Despite its efficiency, CsA can expose to therapeutic failure or to toxicity because of underdosing or overdosage. So, many techniques of monitoring CsA in blood were used, the referance one is the chromatographic technique then, the automated techniques: fluorescence polarization immunoassay (FPIA) and chimiluminescent microparticle immunoassay (CMIA). In this study, we aimed to compare the results of CsA concentrations measured by the two automised techniques. Statistical studies showed that the two techniques were repeatable and reproductible. Results obtained by FPIA were slightly higher than those obtained by CMIA but without a significative difference. In conclusion, FPIA technique could be used to measure CsA blood concentration in replacement of CMIA in case of technical problems.

Vancomycin therapeutic drug monitoring in cerebrospinal fluid.

Vancomycin penetrates poorly through the blood-brain barrier. Determination of vancomycin concentration in plasma is recommended. In contrast, its determination in cerebrospinal fluid (CSF) is rarely performed. We report the case of a 74-year-old man with post traumatic meningitis with vancomycin concentration measured in CSF.